In an electronic device such as a semiconductor device, a porous film may be used. As the porous film, for example, a film formed of a low dielectric constant material such as a SiOC film is used. In manufacturing of such an electronic device, a process is performed in which a fine pattern formed in a photoresist by lithography is transferred to a hard mask such as a TiN film, a SiO2 film, or a Si3N4 film by plasma etching, as necessary, and the pattern is subsequently transferred to the porous film.
In the plasma etching of the porous film, radicals are generated by exciting a gas for etching in a processing chamber of a plasma processing apparatus. The radicals may enter pores of the porous film to damage the porous film. For this reason, there have been proposed some technologies for protecting the porous film from the radicals.
For example, Reference 1 (Liping Zhang et al., “Damage Free Cryogenic Etching of a Porous Organosilica Ultralow-k Film”, ECS Solid State Lett. 2013 volume 2, issue 2, N5-N7) describes a technology in which the porous film is etched under an extremely low temperature to condense a reaction product in the porous film. In this technology, the reaction product condensed in the porous film restrains the radicals from entering the porous film. In order to condense such a reaction product, a temperature at the time of etching the porous film is set to be lower than or equal to −70° C.
In addition, Reference 2 (Markus H. Heyne et al., “Quantitative characterization of pore stuffing and unstuffing for postporosity plasma protection of low-k materials”, Journal of Vacuum Science & Technology B32, 062202 (2014)) describes a technology in which the porous film is permeated with a polymethylmethacrylate resin (PMMA), and the PMMA restrains the radicals from entering the porous film. In this technology, after the etching of the porous film is finished, the PMMA is removed by a plasma process using a mixed gas of a hydrogen gas and a helium gas, or by a post-treatment such as laser annealing.